1. Field of the Invention
This invention relates to a diagnostic probe for bacteria based upon highly specific nucleotide repeat sequences, and more specifically to diagnostic test kits for this purpose.
2. Background
In 1982, the present inventors described, for the first time, a DNA sequence (30-40 bp long), which is highly repeated in the genome of Escherichia coli and Salmonella typhimurium (about 1000 times) [Higgins, C. F., Ferro-Luzzi Ames, G., Barnes, W. M. Clement, J. M. and Hofnung M. (1982) Nature 298: 760-762]. These sequences are referred to as a Palindromic Unit or PU. Their primary sequence conservation is 80%.
Since then, a small difference was noticed in the PU consensus sequences between E. coli and S. typhimurium. This difference is an additional guanine residue in the Salmonella PU sequences. This was a preliminary indication that the PU sequences exhibit species-specificity.
Only a few families of highly repetitive DNA sequences have been described so far in bacteria. Like PUs, they display a tight species specificity. By hybridization, the 26-bp repetitive sequence family of Neisseria spp. (at least 20 copies per genome) was not found in various other gram-negative bacteria [Correia, F. F., Inouye, S. and Inouye, M. (1986) J. Bacteriol. 167, 1009-1015]. A repetitive DNA sequence family from Borderella perrussia also appears to be species-specific [MacPheat, W. L. and MacNally, T. (1987) FEMS Lett. 41:357-360].
Recently, hybridization experiments with E. coli PU DNA as a probe showed that only DNA from enterobacteriaceae close to E. coli hybridized with good efficiency. These experiments will be mentioned, as unpublished data, in a review in Trends in Genetics. Such research allowed the present inventors to determine that the PU specificity could be used for the detection and the identification of bacteria with DNA probes corresponding to PU sequences.
From the above observations concerning enterobacteriaceae and B. pertussis repeated sequences, it appears that the presence of species-specific highly repetive DNA sequences is a general phenomenon among bacteria. Thus, the present invention relates to the use of species specific highly repetitive sequences as specific diagnostic probes. These type of bacterial probes should provide diagnostic assays which are more sensitive than assays with probes corresponding to low copy number genes.